Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare openWorldHint=true, not idempotent, not read-only and not destructive; the description adds the size/format ceiling, the downstream key consumed by create_video, and the hard rights gate that blocks the call. That gating consequence and the mandatory user-consent step are real context beyond the annotations, though it doesn't discuss failure modes, duplicate uploads, or what happens to a stored image later.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The purpose and the alternative tool are front-loaded in the first clause, which is good, but the sentence then runs on through a verbatim legal notice before closing with 'and get their OK.' The notice must be reproduced for the user, so it earns its place, yet the single run-on construction makes the actionable instruction ('get their OK') easy to lose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With only two parameters and no output schema, the description covers the essentials: input constraints, the consent procedure, the returned reference_image_key, and the sibling alternative. Missing only minor operational detail such as whether re-uploading the same URL yields the same key (relevant given idempotentHint=false).

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so both parameters are already documented in structured form. The description does add meaning for rights_confirmed (it holds the exact notice text the agent must present), but image_url is largely a restatement ('public https link straight to a PNG or JPEG') of the schema's own wording.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Store a reference image') with the accepted source (public https link), accepted formats (PNG/JPEG, max 10 MB), and what it produces (a reference_image_key for create_video). It also distinguishes itself from the sibling get_reference_upload_page by naming the case that tool covers (photos on the user's device).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly routes the agent: use this tool for a public link, use get_reference_upload_page for files on the device. It also states the precondition sequence — show the user the rights notice, get their OK, then set rights_confirmed — so there is no ambiguity about when the call is legitimate.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.